In this paper, a multispecies approach for the reactive transport modelling in cementitious materials is proposed. It considers the thermodynamic equilibria in the material during the transport that reflect the liquid – solid interactions and the dissolution/precipitation of solid phases (minerals): dissolution and precipitation of Portlandite and C-S-H. The ion fluxes during the transport are calculated using the Nernst-Planck equation that considers the natural diffusion under a concentration gradient, the migration under an electrical field, and the chemical activity. The model proposed is applied to simulate the standard chloride migration test on two cement pastes. The first paste is based only on Portland cement, while the second paste is composed of fly ash. Numerical results of fluxes of Cl-, Na+ and K+ at the steady state are used to calculate the corresponding effective ion diffusion coefficients in the material studied.